40

How can I convert a bytes32 to a string? Does anyone has a magic function or library which does it?

4

11 Answers 11

15

Based on the latest compiler version 0.4.24, I use the following.

function convertingToString()public returns(string){
bytes32 memory hw = "Hello World";
string memory converted = string(hw);
return converted;
}

Using explicit conversion to carry it out. The reverse is also possible.

For versions 0.5.0+ please use (tested from 0.5 to 0.7.2 - it is likely that it will continue to work past 0.7.2):

function bytes32ToString(bytes32 _bytes32) public pure returns (string memory) {
        uint8 i = 0;
        while(i < 32 && _bytes32[i] != 0) {
            i++;
        }
        bytes memory bytesArray = new bytes(i);
        for (i = 0; i < 32 && _bytes32[i] != 0; i++) {
            bytesArray[i] = _bytes32[i];
        }
        return string(bytesArray);
    }
4
  • 12
    This does not work in solidity version 0.5.0+ Jan 4, 2019 at 14:38
  • 1
    and what does?? Feb 6, 2020 at 11:11
  • 2
    updated for solidity version past 0.5.0 Oct 8, 2020 at 11:37
  • 3
    does not work getting this error ` Failed to decode output: null: invalid codepoint at offset 2; missing continuation byte (argument="bytes", value={"0":91,"1":218,"2":113,"3":98,"4":184,"5":77,"6":255,"7":114,"8":27,"9":203,"10":143,"11":119,"12":114,"13":120,"14":180,"15":136,"16":222,"17":216,"18":209,"19":71,"20":82,"21":100,"22":212,"23":54,"24":28,"25":107,"26":10,"27":191,"28":204,"29":42,"30":153,"31":168}, code=INVALID_ARGUMENT, version=strings/5.1.0) ` was trying to convert this string 0x5bda7162b84dff721bcb8f777278b488ded8d1475264d4361c6b0abfcc2a99a8 Jun 29, 2021 at 16:33
30

Here's one:

function bytes32ToString(bytes32 x) constant returns (string) {
    bytes memory bytesString = new bytes(32);
    uint charCount = 0;
    for (uint j = 0; j < 32; j++) {
        byte char = byte(bytes32(uint(x) * 2 ** (8 * j)));
        if (char != 0) {
            bytesString[charCount] = char;
            charCount++;
        }
    }
    bytes memory bytesStringTrimmed = new bytes(charCount);
    for (j = 0; j < charCount; j++) {
        bytesStringTrimmed[j] = bytesString[j];
    }
    return string(bytesStringTrimmed);
}

To test, here it is combined with how to concatenate an array of bytes32. Paste the following in Remix.

contract C {
    function bytes32ToString(bytes32 x) constant returns (string) {
        bytes memory bytesString = new bytes(32);
        uint charCount = 0;
        for (uint j = 0; j < 32; j++) {
            byte char = byte(bytes32(uint(x) * 2 ** (8 * j)));
            if (char != 0) {
                bytesString[charCount] = char;
                charCount++;
            }
        }
        bytes memory bytesStringTrimmed = new bytes(charCount);
        for (j = 0; j < charCount; j++) {
            bytesStringTrimmed[j] = bytesString[j];
        }
        return string(bytesStringTrimmed);
    }

    function bytes32ArrayToString(bytes32[] data) returns (string) {
        bytes memory bytesString = new bytes(data.length * 32);
        uint urlLength;
        for (uint i=0; i<data.length; i++) {
            for (uint j=0; j<32; j++) {
                byte char = byte(bytes32(uint(data[i]) * 2 ** (8 * j)));
                if (char != 0) {
                    bytesString[urlLength] = char;
                    urlLength += 1;
                }
            }
        }
        bytes memory bytesStringTrimmed = new bytes(urlLength);
        for (i=0; i<urlLength; i++) {
            bytesStringTrimmed[i] = bytesString[i];
        }
        return string(bytesStringTrimmed);
    }    
}

Click "Create". Then in bytes32ToString field enter "0x0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef" and click bytes32ToString.

In bytes32ArrayToString field enter ["0x0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef"] and click bytes32ArrayToString.

Both will show same result (ABI encoding): Result: "0x000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000200123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef"


Here's another example. In bytes32ToString field enter "0xc3b6" and click bytes32ToString. You will get ö.

enter image description here

6
  • I used the bytes32ToString function from above, but I obviously doesn't work with special characters such as ö ä ü etc. Is there a way to use this function with special characters?
    – Bumblebee
    Apr 20, 2017 at 10:02
  • @Bumblebee I added an example for ö and it works. If still needed, probably ask a separate question. (The input or decoding the output might be your problem.)
    – eth
    Apr 21, 2017 at 2:31
  • I am trying your bytes32ArrayToString with a fixed bytes32[10], but it seems I throw an invalid opcode if I use 8-10 full slots of the array. Meaning I have a test for abcdefghijklmnopqrstuvwxyzabcdef (32 characters) 10 times in an array and pass that in, but it throws. If I have 7 or less it works. Any idea why?
    – The Nomad
    Nov 12, 2017 at 12:49
  • @TheNomad Not sure. Suggestions, try once instead of 10 times, and post a new question (a Remix or ethfiddle link might help).
    – eth
    Nov 19, 2017 at 19:37
  • 1
    @Russo It's not clear what you're trying to do in Python; Stackoverflow is a better fit for questions about converting from different Python types.
    – eth
    Jun 3, 2018 at 17:13
25

As of feb 2021 you can do

bytes32 foo = "hello";
string memory bar = string(abi.encodePacked(foo));
3
  • 1
    As soon as StackOverfloor gets the system vote from Medium, I'll give other 10 upvotes. May 23, 2021 at 2:53
  • 3
    Failed to decode output: null: invalid codepoint at offset 2; missing continuation byte (argument="bytes".... Jun 29, 2021 at 15:25
  • unfortunately it keeps zero padding which might be a problem in some cases..
    – Ossip
    Apr 29 at 12:47
11

How to convert a bytes32 to string:

pragma solidity ^0.4.15;

contract Bytes32ToString {

function bytes32ToStr(bytes32 _bytes32) public pure returns (string) {

    // string memory str = string(_bytes32);
    // TypeError: Explicit type conversion not allowed from "bytes32" to "string storage pointer"
    // thus we should fist convert bytes32 to bytes (to dynamically-sized byte array)

    bytes memory bytesArray = new bytes(32);
    for (uint256 i; i < 32; i++) {
        bytesArray[i] = _bytes32[i];
        }
    return string(bytesArray);
    }

}
2

Like @e18r already mentioned, the simplest way to do it without having to write all these crazy functions like everyone else is answering with (and would cost more gas), just do:

string(abi.encodePacked(bytes32));

1
  • unfortunately it seems to keep zero padding which might be a problem in some cases.
    – Ossip
    Apr 29 at 12:47
2

It's recommended you convert a bytes32 to a string using Web3.js to avoid gas costs. To do this, you would get the value of the bytes32 from Solidity to the front end then do:

web3.utils.hexToString(bytes32);

This will convert the bytes32 to a string that you can then see and use in your frontend dApp.

1

In version 0.5.0 and above i ended up with using Viktor answer How to convert a bytes32 to string but removing the zeros otherwise you will end up with

'ERC20\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000'

instead of

'ERC20'

This is the code:

/* bytes32 (fixed-size array) to string (dynamically-sized array) */
function bytes32ToString(bytes32 _bytes32) public pure returns (string memory) {
        uint8 i = 0;
        while(i < 32 && _bytes32[i] != 0) {
            i++;
        }
        bytes memory bytesArray = new bytes(i);
        for (i = 0; i < 32 && _bytes32[i] != 0; i++) {
            bytesArray[i] = _bytes32[i];
        }
        return string(bytesArray);
    }
0

Here's how I'm doing it:

function char(byte b) returns (byte c) {
    if (b < 10) return byte(uint8(b) + 0x30);
    else return byte(uint8(b) + 0x57);
}


function bytes32string(bytes32 b32) returns (string out) {
    bytes memory s = new bytes(64);

    for (var i = 0; i < 32; i++) {
        byte b = byte(b32[i]);
        byte hi = byte(uint8(b) / 16);
        byte lo = byte(uint8(b) - 16 * uint8(hi));
        s[i*2] = char(hi);
        s[i*2+1] = char(lo);            
    }

    out = string(s);
}
0
    // SPDX-License-Identifier: MIT
    pragma solidity ^0.8.7;
    contract stringtobytes{
        function set(string memory  _a)public pure returns(bytes memory){
            return bytes(_a);
        } 
         function set1(bytes memory  _a)public pure returns(string  memory){
            return string(_a);
        } 

}

// you can convert strings to bytes(in decimal format) and vice versa with below code

//1- bytes1=8bit=2decimal

//2 bytes2=16bit=4decimal

//3 bytes3=24bit=6decimal

//4 bytes=dynamic array and reference value

1
  • 1
    The question is about conversion from bytes32 to string, and your example doesn't work for that.
    – Ismael
    Feb 3 at 13:34
0

A more gas-efficient method based on this answer (For versions 0.5.0+):

function toString(bytes32 source)
    internal
    pure
    returns (string memory result)
{
    uint8 length = 0;
    while (source[length] != 0 && length < 32) {
        length++;
    }
    assembly {
        result := mload(0x40)
        // new "memory end" including padding (the string isn't larger than 32 bytes)
        mstore(0x40, add(result, 0x40))
        // store length in memory
        mstore(result, length)
        // write actual data
        mstore(add(result, 0x20), source)
    }
}

This solution is using assembly to copy data to memory instead of for looping.

0

Just in case, if you want to convert bytes32 to ASCII string, you can use the OpenZeppelin Strings library.

https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2504

Strings.toHexString(uint256(tokenIdSeed), 32),

The output should be like

0xd8df8ecd5432b247d2fc2beb0619d637e9de0df7512bd36220582deda9a1df6e 

(this is just covert hexadecimal value of the bytes32 to string)

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